Switching mechanism

ABSTRACT

A plug in relay is provided in which the switches are mounted directly on the plug in base, the supports for the switch blades and stationary contacts extending through the base and forming the plug in terminals. The switches are positively operated by levers on each side of the blades. These levers have camming surfaces which are acted on by abutments formed on a slide attached to a solenoid. The camming surfaces are non-linear to cause contact closure at a relatively slow rate with high initial contact pressure to prevent contact bounce. Strain relief for overtravel is provided by movable pivots for the levers held in normal position by a spring.

United States Patent 1191 Har s 1 51 Jan. 22, 1974 [5 SWITCHING MECHANISM 3,717,829 2/1973 Flaherty 335/202 [75] Inventor. John L. Harris, Clearwater, Fla. Primary Examiner Harold Bmome [73] Assignee: Deltrol Corp., Bellwood, I11. 221 Filed: Oct. 24', 1972 [57] A plug 1n relay is provided 1n which the switches are PP 300,122 mounted directly on the plug in base, the supports for the switch blades and stationary contacts extending 521 US. (:1. 335/193, 335/192 through the base and forming the Plug in terminals 51 1111. C1. 110111 3/60 The Switches are Positively Operated by levers each 5 Field f Search" 335/193, 192, 133, 202,189 side of the blades. These levers have camming sur- 335/194, 190, 200; 200/153 V, 153 H 164 faces which are acted on by abutments formed on a slide attached to a solenoid. The camming surfaces are 5 References Cited non-linear to cause contact closure at a relatively slow UNITED STATES PATENTS rate with high initial contact pressure to prevent I contact bounce. Strain relief for overtravel is provided by movable pivots for the levers held in normal posi- 2I977I430 3/1961 Walder 200 153 H by a 3,087,031 4/1963 Spinelli et a1. 335/133 19 Claims, 10 Drawing Figures SWITCHING MECHANISM CROSS REFERENCE TO RELATED APPLICATIONS The invention presented in this application utilizes certain basic features claimed in my copending application Ser. No. 192,533 filed Oct. 26, 1971.

BACKGROUND OF THE INVENTION In small general purpose electro-mechanical relays it is common to use a clapper type electro-magnet. The

clapper carries one or more switch blades which carry movable contacts extending between stationary contacts mounted on a base forming part of the relay.

This type of relay has a number of shortcomings, one being contact bounce. When the electro-magnet is energized the movable contact is moved swiftly from one stationary contact to the other. When it first strikes the stationary contact the flexible switch blade has no load and no force is in existence opposing the bounce. As a result, the contacts bounce several times before the clapper reaches the end of its stroke. This is damaging to the contacts on high inrush loads such as tungsten lights or electric motors.

This type of relay also has the disadvantage of requiring pigtail leads for attaching the movable blades to terrninals on the panel. In addition, in manufacture the movable blades must be adjusted for a given contact pressure. This requires checking and rechecking with a gram gage which is a costly step.

In many applications where duty cycles are high and quick replacement is needed from time to time, relays are mounted on plug in bases. This requires soldering a lead from each of the relay terminals to terminals on the plug in base, which is quite expensive.

BRIEF SUMMARY OF INVENTION This invention relates to switching mechanism and more particularly to eIectro-magnetic switches.

One object of the invention is the provision of a small low cost plug in type relay in which the switches are integral with the plug in terminals, requiring no pigtail leads or plug in connecting leads.

Another object of the invention'is the provision of a switching mechanism in which contact bounce is eliminated or greatly reduced.

A further object is the provision of a switching mechanism which can be quickly assembled without the need of skilled assembly workers.

In the preferred form of the invention, the switch blades and stationary contacts are mounted directly on the plug in base. The supports for these parts extend through the base and the external portions are plug in terminals. When free, the switch blades have no tension and the movable contacts are midway between the stationary contacts. No measurement of contact pressure is required.

Each blade is operated by two levers extending parallel with the blade, one lever contacting the blade to force it into engagement with one stationary contact and th other lever forcing the blade into engagement with the outer stationary contact. These levers are operated by a solenoid actuated slide having abutments riding on camming surfaces on the levers. Energization of the solenoid moves the slide to one position, camming one lever to close its contact and releasing the other lever. Deenergization moves the slide to its other position closing the. other contact.

In order to allow overtravel movement of the slide after the contacts engage, the levers are mounted on floating or movable pivots. These are held in normal position against stops by a spring which is preloaded by pressing the levers against the stops. After the slide moves one lever to clost its contact, further movement causes the pivot point to move against the action of the spring. The tension on the spring determines the Contact pressure.

The camming surfaces on the levers are formed with a sharp rise in the portion moving the blade through the gap and with a small-rise as the contacts engage. This gives the solenoid mechanical advantage when needed, allowing the use of considerable initial contact pressure to resist contact bounce. It also slows the contact engagement reducing the tendency to bounce. The mass of the lever itself also opposes the tendency to bounce and the combined result is bounceless contact closure.

Other objects of the invention will appear from the following detailed description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a top external view of a device embodying the invention.

FIG. 2 is an elevation of FIG. 1.

FIG. 3 is a side view of FIG. 2.

FIG. 4 is a bottom view showing the external connections.

FIG. 5 is a top view of the base and switch subassembly before insertion of the switch operating mechanism.

FIG. 6 is a top view with the cover removed and showing the switching mechanism in the position assumed when the solenoid is deenergized.

FIG. 7 is a sectional view taken on line 77 of FIG. 6 and with certain parts omitted.

FIG. 8 is a view similar to FIG. 7 but showing the parts in the positions assumed when the solenoid is energized.

FIG. 9 is a sectional view taken on line 9-9 of FIG. 8 and with certain parts omitted.

FIG. 10 is a sectional view taken on line l0-10 of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 to 5, the switching mechanism includes a plastic molded housing generally indicated as 1 having a bottom wall 2, side walls 3 and 4 and end walls 5 and 6. This housing is open at its top and is formed with bosses 7, 8 and 9 (FIG. 5) which receive screws 10 securing cover 11 in place. This cover supports a solenoid generally indicated as 12 including a molded coil 13, a plunger 14 and a return spring 15. The plunger 14 is formed with a reduced portion 16 which receives an upstanding arm 17 of a sliding member inside the enclosure.

As shown in FIG. 5, the housing 1 is divided into two separate compartments l9 and 20 by a divider 21. The compartment 19 contains a switch 22 including a switch blade 23 carrying a double contact 24. The switch blade 23 is supported on a terminal member 25 which extends through the bottom wall of the housing and is formed to receive a female quick connect terminal which may form part of a plug in socket not shown.

The double contact 24 selectively engages stationary contacts 26 and 27 carried by terminal members 28 and 29 which extend downwardly through the bottom wall of the case and serve as terminals for external connections. Preferrably the bottom wall 2 of the housing is molded with bosses 30 through which the terminal members extend. These bosses provide extra material for maintaining the terminals in proper alignment.

The compartment 20 contains a switch 32 which is identical with the switch 22 previously described. This switch includes a switch blade 23a and a double contact 24a cooperating with stationary contacts 26a and 27a. It should be noted that when switch blades 23 and 23a are free as shown in FIG. 5, the contacts 24 and 24a are midway between the, stationary contacts.

As shown in FIGS.'5 and 9, the housing 1 is formed with a passage 33. This passage accommodates the solenoid leads 34 which extend through the unit and which are attached to quick connect terminals 35 and 36 suitably secured in the bottom wall of the housing. This arrangement gets the leads to the plug in base of the timer within the confines of the base thus protecting the leads and also minimizing the space requirements for mounting the unit.

Means are provided for operating switches 22 and 32 inside the case from motion of the solenoid plunger 14. The upstanding arm 17 which fits into the solenoid plunger is'part of a solenoid slide member 38 which is mounted in the housing 1 just under the cover 11. This slide is preferrably molded of transparentmaterial so that the operation of the mechanism can be viewed be fore the cover 11 is put in place. Slide 38 is movable from right to left and vice versa as seen in FIGS. 6 and 8. It is guided in this movement by a tongue 39 (FIGS. 7 and 9) which is molded integral with the slide and which fits closely in a groove 40 formed in the divider 21. This slide is also guided at its outer edges by cars 42 and 43 which extend into slots 44 and 45 formed in the side walls of the enclosure. As shown in FIG, 9 the upstanding arm 17 is bifurcated at 46 for fitting into the notch 16 of solenoid plunger 14. It will be apparent that when the solenoid 12 is energized, the slide 38 will move to the left against the action of spring 15. When the solenoid is deenergized, the spring l urges the slide to the right as seen in FIG. 6.

The slide 38 includes two identical drop-out actuators 46 which extend downwardly into contact with camming surfaces 47 of drop-out switch operators or levers 48. Each lever 48 includes an operating portion 49 which urges the switch blade 23 or 23a upwardly as shown in FIG. 6. Each lever 48 also includes a movable pivot means comprising opposed contacting surfaces 50 and 51 which engages a stationary abutment 52 molded integral with the housing. The contact surfaces 50 and 51 are joined by a stop surface 53 which is engageable with the end 54 of abutment 52 to provide a stop means for limiting the travel of the movable pivot means under the action of spring 55. (See FIG. 8).

The slide 38 also includes pull-in abutments 57 which extend downwardly into contact with camming surfaces 58 of pull-in switch operators or levers 59. Each lever 59 includes an operating portion 60 adapted to engage its respective switch blade adjacent the contact and push the blade down for closing the lower contacts as seen in FIG. 8. Each lever 59 also includes movable pivot means comprising opposed contact surfaces 61 and 62 engaging a stationary abutment 63 molded integral with the enclosure. A stop surface 64 is arranged to engage with the end 65 of abutment 63 to limit the movement of the movable pivot means under the action of spring 55 as shown in FIG. 6.

As shown in FIGS. 7 and 10, the lever 59 includes a relatively wide portion 67 which fits over the abutment 63 between a shoulder 68 and the slide 38. The shoulder 68 forms the top of an abutment 69 molded in the enclosure. It will be apparent that the camming surface 58 of the lever is located on the relatively wide portion 67 and is thus engaged by the abutment 57 on the slide over a substantial surface which eliminates any tendency to rock. The portion of the operator 59 beyond the camming surface is preferrably reduced as at 70 and is guided between a stationary abutment 71 molded on the case and a movable abutment 72 carried by the solenoid slide 38. The drop-out switch operators are formed and guided in a similar manner to the pullin operators just described.

The drop-out and pull-in operators are molded with circular opposed spring guides 74 and 75. These guides support the compression spring 55 which urges both levers toward engagement of the limiting stops formed on the floating pivots.

OPERATION With the parts in the positions shown in FIGS. 2 and 6, the solenoid is deenergized and the spring 15 has urged the solenoid slide to the right causing the right hand end of the slide to engage end wall 6 of the enclosure. The camming extensions or actuators 57 on the solenoid slide have moved away from the camming surfaces 58 on the pull-in levers 59, and these levers therefore exert no force on the switch blades 23 and 23a. Also each spring 55 is free to urge these levers to bring their stop surfaces 64 into engagement with the ends 65 of the abutments 63.

The drop-out movement of the solenoid slide has brought camming abutments 46 into engagement with the camming surfaces 47 on the switch operators. This has caused each operator 48 to rock about the point of engagement with the camming surfaces 47 urging the switch blades upwardly engaging the top contacts as shown in FIG. 6. Over travel movement of the solenoid slide after contact engagement has caused the stop surfaces 53 on each operator to disengage its corresponding stop surface 54. This has resulted in additional compressing of spring 55 after contact engagement occurs.

When the solenoid is energized, the plunger pulls the solenoid slide to the left to the position shown in FIG. 8. During this motion, the drop-out abutments 46 on the slide pulls away from the camming surfaces 47 allowing the operators 48 to rotate clockwise about their movable pivots and thus disengage their respective switch blades. This same motion allows the stop surfaces 53 on each operator to engage the stop surface 54. As the camming surfaces 47 are being released by camming abutments 46 on the slide, the camming abutments 57 are engaging the camming surfaces 58 of the pull-in switch operators 59. This rocks the operators 59 clockwise about their movable pivots and causes them to engage and drive the switch blades downwardly until the lower contacts are engaged. After engagement takes place, continued over travel movement of the solenoid slide causes the operators 59 to rock about the point of camming engagement thus moving each movable stop surface 64 away from stationary stop surface 65 and compressing spring 55.

It will be apparent that the tension of spring 55 serves to determine the contact pressure applied at the contacts and also provides a strained relief permitting over travel movement of the slide and insuring seating of the solenoid plunger.

When the solenoid is deenergized, the slide moves to the right under the action of the return spring 15. Initial movement of the slide causes disengagement of the camming surfaces 57-58 and allows spring 55 to reengage the stop means 62-64. This disengagement of the camming surfaces 57-58 thus allows each switch operator 59 to disengage its respective switch blade. At the same time that cam surfaces 57-58 are releasing, the drop-out cam surfaces 4647 are engaging and rotating levers 48 about their pivots. This motion drives the switch blades from the neutral positions shown in FIG. 5 to their upper positions as shown in FIG. 6. After the contacts engage, further outward movement of the slide causes the levers 48 to pivot around their blade engaging portions 49, this motion being permitted by sliding of the contacting surfaces 50 and 51 on abutment 52. This action in turn is permitted by yielding of the over travel spring 55. At the end of the stroke of the solenoid slide, a gap exists between the stop surface 53 on the lever 48 and the end 54 of abutment 52.

As the solenoid slide moves to the right due to force from the return spring 15, the initial function of the camming surfaces 46-47 is to move the operator upwardly first closing the air gap between the operator and blade and then moving the blade through its air gap as shown in FIG. 5 unit] the contacts engage. This movement of the switch operator requires a minimum of force at the time when the solenoid spring is compressed and a maximum force from the spring is available. As the slide continues its travel, it is compressing the over travel spring 55 and thus resistence-to movement of the slide is increasing at a time when the force available from spring is decreasing. For this reason the camming surface 47 is characterized to provide a non-linear rate of motion of the switch operator lever relative to motion of the driving camming surface 46. This curveis arranged to be steeper at the beginning of the stroke and to level out as the stroke continues, thus providing maximum movement of the lever per increment of movement of the slide at the beginning of the stroke and reduces the rate of travel of the lever as the slide continues its motion. This arrangement compensates for the increasing resistence to movement and the decreasing force available as the movement continues. This reduces the amount of force needed from the solenoid spring and this in turn reduces the size of the solenoid required. In addition this arrangement provides for rapid motion of the mechanism when it is taking up the air gaps and reduces the speed of the operator at the point of contact engagement. This reduction in speed of the contact at the time of engagement reduces the tendency of the contact to bounce. In addition at the time of contact engagement, the lever 48 is being urged in a non-yielding manner by the engagement of the surfaces 46-47. The point of contact of the lever with the switch blade 23 is immediately adjacent the contact so that a minimum amount of flexing of the switch blade can take place between the contact and the operating portion 49 of lever 48. In order for the contacts to bounce, the bouncing effect must overcome the inertia of the lever 48 itself and also cause the stop surface 53 on the lever to disengage from the end of abutment 52. This combination of reduction in speed at contact engagement, engaging of the blade adjacent the contact, the non-yielding pivot action at cam surfaces 46-47, the inertia of the lever itself, and the effect of spring 55 all combine to minimize contact bounce.

When the solenoid pills, in the camming surfaces 57-58 provide for rapid motion during the initial portion of the stroke and a reduction in speed at the point of contact engagement. The curve on cam surface 58 is preferrably formed with a higher slope at the end of the stroke than the curve 47 of the drop-out operator 48. The reason for this is that on the pull-in stroke of the solenoid, the force available builds up as the air gap closes, requiring less compensation than on the dropout camming curve.

As shown in FIG. 5 when the switch blades 23 are free, they locate the movable contacts midway between the stationary contacts. In other words there is an air gap on both sides. This eliminates setting blade tension with gram gauges and thus reduces manufacturing costs. In addition it provides for a slow break which is advantageous on AC. loads in that it reduces arcing. It will be apparent that as the switch operator is released from contact engaging position, the bias of the switch blade itself is the thing that causes the contacts to disengage. This disengaging force is small compared with the inertia of the blade and contacts, and thus the initial movement of the contact is slow. This causes the arc to be small at the time the current passes through zero and thus the arc is extinguished before it is drawn out to far.

From the foregoing it will be apparent that the invention provides a simple, compact and easily constructed device which is capable of carrying extremely high loads for its size due to the substantial elimination of contact bounce and arcing.

While a preferred form of the invention is shown and described herein, it is obvious that numerous modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. In a switching mechanism, a stationary contact, a movable contact cooperating therewith, means for moving said movable contact into engagement with the stationary contact comprising a lever having movable pivot means, said lever having a contact operating portion spaced from the pivot means, stop means for limiting motion of the pivot means in one direction, spring means holding the pivot means against said stop means with a predetermined force, and means including power means for applying a force to the lever causing the lever to rotate until the contacts engage with a contact pressure determined by the spring means, at which time the spring means allows the movable pivot means to separate from the stop means permitting over-travel movement of the power means, said power means including a slide mounted for movement transverse to movement of the lever, and camming means between the slide and lever causing movement of the lever from movement of the slide.

2. The combination recited in claim 1 in which the camming means reduces the rate of travel of the lever per increment of movement of the slide in contact engaging direction.

3. In a switching mechanism, a stationary contact, a movable contact cooperating therewith, means for moving said movable contact into engagement with the stationary contact comprising a lever having movable pivot means, said lever having a contact operating portion spaced from the pivot means, stop means for limiting motion of the pivot means in one direction, spring means holding the pivot means against said stop means with a predetermined force, means including power means for applying a force to the lever causing the lever to rotate until the contacts engage with a contact pressure determined by the spring means, at which time the spring means allows the movable pivot means to separate from the stop means permitting over-travel movement of the power means, said movable pivot means comprising a stationary abutment means and contact surfaces on the lever engaging said stationary abutment means, said contact surfaces being slidable on said abutment means.

4. The combination recited in claim 3 in which the contact surfaces on the lever face each other and the stationary abutment also serves as a stop for the pivot means by engaging a stop surface on the lever which is between the contact surfaces.

5. The combination recited in claim 4 in which the spring means bears on the'lever adjacent the stationary abutment which substantially neutralizes any turning moment of the spring means on the lever about the movable pivot means.

6. The combination recited in claim 4 in which the movable contact is carried by a switch blade extending generally parallel with the lever and in which the power means includes a slide mounted for movement generally parallel to the lever, and camming means causing movement of the lever to operate the switch blade from movement of the slide.

7. In a double throw switching mechanism, the combination of, a switch blade anchored at one end and having contact surfaces on both sides, a first stationary contact opposing one contact surface and a second stationary contact opposing the other contact surface, a first lever extending generally parallel with the switch blade, said first lever having an operating portion engaging the blade on one side thereof adjacent one contact surface and having a movable pivot means spaced from said operating portion, a second lever extending generally parallel with the switch blade, said second lever having an operating portion engaging the blade on the other side thereof adjacent the other contact surface and having movable pivot means spaced from said last mentioned operating portion, stop means for limiting motion of both movable pivot means, spring means for holding both pivot means against the stop means with predetermined force, means including power means for selectively applying force to either the first lever or the second lever for engaging one stationary contact or the other with a contact pressure determined by the spring means, the spring means then allowing the affected movable pivot means to separate from its stop means permitting overtravel movement of the power means.

8. The combination recited in claim 7 in which the power means is a slide mounted for movement-generally parallel to the switch blade and levers, and camming means between the slide and both levers causing engagement with one stationary contact when the slide is moved to one position and causing engagement of the other stationary contact when the slide is moved to another position.

9. The combination recited in claim 8 in which the camming means for each lever reduces the travel of that lever per increment of movement of the slide in contact engaging direction.

10. The combination recited in claim 7 in which the movable pivot means comprises a stationary abutment means and contact surfaces on each lever engaging and slidable on the stationary abutment means.

11. The combination recited in claim 7 in which the spring means is a single spring, one end bearing on one of the levers and the other end bearing on the other of said levers.

12. The combination recited in claim 11 in which the movable pivot means and stop means for both levers are in alignment and in which the single spring is in the same alignment, substantially neutralizing any turning moment of the spring means on the levers.

13. In a switching device, the combination of, a base member of insulating material, said base member being formed with a main wall, terminal member means mounted on the main wall, said terminal member means being adapted for connection to external wiring on one side of the main wall and having a switch blade mounting surface on the other side thereof extending substantially perpendicular to the main wall, a switch blade mounted on said mounting surface and extending generally parallel to said main wall, said switch blade carrying a movable contact, a second terminal member means mounted on the main wall, said second terminal member means carrying a stationary contact in engaging relationship with said movable contact, a cover plate mounted on the base member, said cover plate being generally parallel to the main wall and spaced from the switch blade, operating means for moving the switch blade to engage and disengage the contacts, said operating means including a movable memberunder, adjacent, and generally parallel to the cover plate and movably mounted for moving parallel thereto, and power means on the cover plate for actuating said movable member.

14. The combination recited in claim 13 in which the operating means for the switch blade includes a lever having movable pivot means, said pivot means being carried by the base member, stop means also carried by the base member for limiting motion of the movable pivot means in one direction, and spring means holding the pivot means against the stop means with a predetermined force, said lever having one portion engaging the switch blade on the side opposite the stationary contact and another portion engaged by the movable member.

15. The combination recited in claim 14 in which the movable member is a slide and actuates the lever by a camming action arranged to reduce the travel of the lever per increment of movement of the slide in contact engaging direction.

16. The combination recited in claim 13 in which the operating means for the switch blade includes first and second levers extending generally parallel with the blade, the first lever engaging one side of the blade and the second lever engaging the other side of the blade, said levers being actuated by said movable member.

17. The combination recited in claim 16 in which the movable member is a slide and actuates the levers by a camming action, and strain relief means for at least one of said levers, said strain relief means comprising movable pivot means for said one lever.

18. The combination recited in claim 16 in which at least one of the levers includes strain relief means allowing continued movement of the movable member after the contacts engage, said strain relief comprising movable pivot means, stop means therefore and spring means holding the movable pivot means against the stop means.

19. In a switching mechanism, a stationary contact, a movable contact cooperating therewith, a flexible switch blade, a stationary support, a first portion of the switch blade being attached to said stationary support and a second portion of said blade being movable and carrying said movable contact, a lever having movable pivot means, said lever having a contact operating portion spaced from the pivot means and arranged to engage the switch blade adjacent the movable contact in a manner to urge said contacts into engagement, stop means for limiting motion of the pivot means in one direction, spring means holding the pivot means against the stop means with a predetermined force, and means including power means for applying a force to the lever causing the lever to rotate until the contacts engage with a contact pressure determined by the spring means, at which time the spring means allows the movable pivot means to separate from the stop means permitting overtravel movement of the stop means. 

1. In a switching mechanism, a stationary contact, a movable contact cooperating therewith, means for moving said movable contact into engagement with the stationary contact comprising a lever having movable pivot means, said lever having a contact operating portion spaced from the pivot means, stop means for limiting motion of the pivot means in one direction, spring means holding the pivot means against said stop means with a predetermined force, and means including power means for applying a force to the lever causing the lever to rotate until the contacts engage with a contact pressure determined by the spring means, at which time the spring means allows the movable pivot means to separate from the stop means permitting over-travel movement of the power means, said power means including a slide mounted for movement transverse to movement of the lever, and camming means between the slide and lever causing movement of the lever from movement of the slide.
 2. The combination recited in claim 1 in which the camming means reduces the rate of travel of the lever per increment of movement of the slide in contact engaging direction.
 3. In a switching mechanism, a stationary contact, a movable contact cooperating therewith, means for moving said movable contact into engagement with the stationary contact comprising a lever having movable pivot means, said lever having a contact operating portion spaced from the pivot means, stop means for limiting motion of the pivot means in one direction, spring means holding the pivot means against said stop means with a predetermined force, means including power means for applying a force to the lever causing the lever to rotate until the contacts engage with a contact pressure determined by the spring means, at which time the spring means allows the movable pivot means to separate from the stop means permitting over-travel movement of the power means, said movable pivot means comprising a stationary abutment means and contact surfaces on the lever engaging said stationary abutment means, said contact surfaces being slidable on said abutment means.
 4. The combination recited in claim 3 in which the contact surfaces on the lever face each other and the stationary abutment also serves as a stop for the pivot means by engaging a stop surface on the lever which is between the contact surfaces.
 5. The combination recited in claim 4 in which the spring means bears on the lever adjacent the stationary abutment which substantially neutralizes any turning moment of the spring means on the lever about the movable pivot means.
 6. The combination recited in claim 4 in which the movable contact is carried by a switch blade extending generally parallel with the lever and in which the power means includes a slide mounted for movement generally parallel to the lever, and camming means causing movement of the lever to operate the switch blade from movement of the slide.
 7. In a double throw switching mechanism, the combination of, a switch blade anchored at one end and having contact surfaces on both sides, a first stationary contact opposing one contact surface and a second stationary contact opposing the other contact surface, a first lever extending generally parallel with the switch blade, said first lever having an operating portion engaging the blade on one side thereof adjacent one contact surface and having a movable pivot means spaced from said operating portion, a second lever extending generally parallel with the switch blade, said second lever having an operating portion engaging the blade on the other side thereof adjacent the other contact surface and having movable pivot means spaced from said last mentioned operating portion, stop means for limiting motion of both movable pivot means, spring means for holding both pivot means against the stop means with predetermined force, meAns including power means for selectively applying force to either the first lever or the second lever for engaging one stationary contact or the other with a contact pressure determined by the spring means, the spring means then allowing the affected movable pivot means to separate from its stop means permitting overtravel movement of the power means.
 8. The combination recited in claim 7 in which the power means is a slide mounted for movement generally parallel to the switch blade and levers, and camming means between the slide and both levers causing engagement with one stationary contact when the slide is moved to one position and causing engagement of the other stationary contact when the slide is moved to another position.
 9. The combination recited in claim 8 in which the camming means for each lever reduces the travel of that lever per increment of movement of the slide in contact engaging direction.
 10. The combination recited in claim 7 in which the movable pivot means comprises a stationary abutment means and contact surfaces on each lever engaging and slidable on the stationary abutment means.
 11. The combination recited in claim 7 in which the spring means is a single spring, one end bearing on one of the levers and the other end bearing on the other of said levers.
 12. The combination recited in claim 11 in which the movable pivot means and stop means for both levers are in alignment and in which the single spring is in the same alignment, substantially neutralizing any turning moment of the spring means on the levers.
 13. In a switching device, the combination of, a base member of insulating material, said base member being formed with a main wall, terminal member means mounted on the main wall, said terminal member means being adapted for connection to external wiring on one side of the main wall and having a switch blade mounting surface on the other side thereof extending substantially perpendicular to the main wall, a switch blade mounted on said mounting surface and extending generally parallel to said main wall, said switch blade carrying a movable contact, a second terminal member means mounted on the main wall, said second terminal member means carrying a stationary contact in engaging relationship with said movable contact, a cover plate mounted on the base member, said cover plate being generally parallel to the main wall and spaced from the switch blade, operating means for moving the switch blade to engage and disengage the contacts, said operating means including a movable member under, adjacent, and generally parallel to the cover plate and movably mounted for moving parallel thereto, and power means on the cover plate for actuating said movable member.
 14. The combination recited in claim 13 in which the operating means for the switch blade includes a lever having movable pivot means, said pivot means being carried by the base member, stop means also carried by the base member for limiting motion of the movable pivot means in one direction, and spring means holding the pivot means against the stop means with a predetermined force, said lever having one portion engaging the switch blade on the side opposite the stationary contact and another portion engaged by the movable member.
 15. The combination recited in claim 14 in which the movable member is a slide and actuates the lever by a camming action arranged to reduce the travel of the lever per increment of movement of the slide in contact engaging direction.
 16. The combination recited in claim 13 in which the operating means for the switch blade includes first and second levers extending generally parallel with the blade, the first lever engaging one side of the blade and the second lever engaging the other side of the blade, said levers being actuated by said movable member.
 17. The combination recited in claim 16 in which the movable member is a slide and actuates the levers by a camming action, and strain relief means for at least one of said levers, said straIn relief means comprising movable pivot means for said one lever.
 18. The combination recited in claim 16 in which at least one of the levers includes strain relief means allowing continued movement of the movable member after the contacts engage, said strain relief comprising movable pivot means, stop means therefore and spring means holding the movable pivot means against the stop means.
 19. In a switching mechanism, a stationary contact, a movable contact cooperating therewith, a flexible switch blade, a stationary support, a first portion of the switch blade being attached to said stationary support and a second portion of said blade being movable and carrying said movable contact, a lever having movable pivot means, said lever having a contact operating portion spaced from the pivot means and arranged to engage the switch blade adjacent the movable contact in a manner to urge said contacts into engagement, stop means for limiting motion of the pivot means in one direction, spring means holding the pivot means against the stop means with a predetermined force, and means including power means for applying a force to the lever causing the lever to rotate until the contacts engage with a contact pressure determined by the spring means, at which time the spring means allows the movable pivot means to separate from the stop means permitting overtravel movement of the stop means. 